[−][src]Crate abi_stable
For Rust-to-Rust ffi, with a focus on creating libraries loaded at program startup, and with load-time type-checking.
This library allows defining Rust libraries that can be loaded at runtime, even if they were built with a different Rust version than the crate that depends on it.
These are some usecases for this library:
-
Converting a Rust dependency tree from compiling statically into a single binary, into one binary (and potentially) many dynamic libraries, allowing separate re-compilation on changes.
-
Creating a plugin system (without support for unloading).
Features
Currently this library has these features:
-
Features the
#[sabi_trait]
attribute,for creating ffi-safe trait objects. -
ffi-safe equivalent of trait objects for any combination of a selection of traits.
-
Provides ffi-safe alternatives/wrappers for many standard library types, in the
std_types
module. -
Provides ffi-safe wrappers for some crates,in the
external_types
module. -
Provides the
StableAbi
trait for asserting that types are ffi-safe. -
Features for building extensible modules and vtables,without breaking ABI compatibility.
-
Checking at load-time that the types in the dynamic library have the expected layout, allowing for semver compatible changes while checking the layout of types.
-
Provides the
StableAbi
derive macro to both assert that the type is ffi compatible, and to get the layout of the type at load-time to check that it is still compatible.
Examples
For examples of using abi_stable
you can look at the readme,
or for the crates in the examples directory in the repository for this crate.
To run the examples generally you'll have to build the *_impl
crate,
then run the *_user
crate (all *_user
crates should have a help message and a readme.md).
Glossary
interface crate
:the crate that declares the public functions and types that
are necessary to load the library at runtime.
ìmplementation crate
:A crate that implements all the functions in the interface crate.
user crate
:A crate that depends on an interface crate
and
loads 1 or more ìmplementation crate
s for it.
module
:refers to a struct of function pointers and other static values,
and implement the RootModule trait.
These are declared in the interface crate
,exported in the implementation crate
,
and loaded in the user crate
.
Rust-to-Rust FFI guidelines.
Types must implement StableAbi to be safely passed through the FFI boundary, which can be done using the StableAbi derive macro.
These are the kinds of types passed through FFI:
-
Value kind: The layout of types passed by value must not change in a minor version. This is the default kind when deriving StableAbi.
-
Opaque kind: Types wrapped in
DynTrait<SomePointer<()>,Interface>
, whose layout can change in any version of the library, and can only be unwrapped back to the original type in the dynamic library/binary that created it. -
Trait objects: Trait object-like types generated using
#[sabi_trait]
, which erase the type of the value they wrap,implements the methods of the trait, and can be unwrapped back to the original type in the dynamic library/binary that created it (if it was constructed to be unerasable and implements Any). -
Prefix kind: Types only accessible through shared references, most commonly vtables and modules, which can be extended in minor versions while staying ABI compatible. by adding fields at the end.
Declaring enums
Adding variants or fields to a variant is disallowed in minor versions.
To represent non-exhaustive enums without fields it is recommended using structs and associated constants so that it is not UB to keep adding field-less variants in minor versions.
Extra documentation
- Unsafe code guidelines:
Describes how to write unsafe code ,relating to this library.
Macros (derive and attribute)
-
sabi_trait attribute macro:
For generating ffi-safe trait objects. -
StableAbi derive macro:
For asserting abi-stability of a type, and obtaining the layout of the type at runtime. -
Prefix-types (using the StableAbi derive macro) :
The method by which vtables and modules are implemented, allowing extending them in minor versions of a library.
Re-exports
pub use abi_stable_derive::StableAbi; |
pub use abi_stable_derive::export_root_module; |
pub use abi_stable_derive::impl_InterfaceType; |
pub use abi_stable_derive::sabi_trait; |
Modules
abi_stability | types and traits related to abi stability. |
const_utils | Utilities for const contexts. |
docs | Documentation for macros,and guides. |
erased_types | Types and traits related to type erasure. |
external_types | Ffi wrapper for types defined outside the standard library. |
library | Traits and types related to loading an abi_stable dynamic library, as well as functions/modules within. |
marker_type | Zero-sized types . |
pointer_trait | Traits for pointers. |
prefix_type | Types,traits,and functions used by prefix-types. |
reexports | Miscelaneous items re-exported from core_extensions. |
reflection | Types and submodules for doing runtime reflection. |
sabi_trait | |
sabi_types | StableAbi types that aren't wrappers for other types. |
std_types | Contains many ffi-safe equivalents of standard library types. The vast majority of them can be converted to and from std equivalents. |
traits | Where miscellaneous traits reside. |
type_level | Types used to represent values at compile-time,eg:True/False. |
utils | Utility functions. |
Macros
declare_root_module_statics | Implements the |
extern_fn_panic_handling | Use this to make sure that you handle panics inside |
impl_get_type_info | Constructs the abi_stable::erased_types::TypeInfo for some type. |
make_item_info | Constructs a abi_stable::abi_stability::type_layout::ItemInfo, with information about the place where it's called. |
package_version_strings | Instantiates a |
rtry | Equivalent to |
rtry_opt | Equivalent to |
tag | Constructs a abi_stable::abi_stability::Tag, a dynamically typed value for users to check extra properties about their types when doing runtime type checking. |
tl_genparams | Use this when constructing a |
type_identity | Allows converting between |
Structs
DynTrait | DynTrait implements ffi-safe trait objects,for a selection of traits. |
Statics
LIB_HEADER | The header used to identify the version number of abi_stable that a dynamic libraries uses. |
Traits
ImplType | An |
InterfaceType | Defines the usable/required traits when creating a
|
StableAbi | Represents a type whose layout is stable. |